Wednesday, August 24, 2011

The Age of the Universe: Part 3

Not all stars stay the same brightness. There is a constant tug-of-war inside a star between the thermonuclear reactions trying to expand the star and gravity trying to hold it all together. In some stars, this swings back and forth pretty dramatically. We all these variable stars.

One kind of variable star is called a Cepheid variable (so named because one of the first identified was in the constellation Cepheus). One of astronomy's unsung heroes, Henrietta Leavitt, discovered that there was a relationship between the amount of time between peaks of brightness (called the period) and the range of brightnesses. So now you could tell how bright one of these stars was by simply measuring how long it took for the star to go from bright to dim to bright again.

With this new tool for measuring the absolute magnitude of a star, Edwin Hubble and his assistant Milton Humason, discovered Cepheid variables in a faint cloud called M31. They were able to determine its distance and discovered that it was over 2 million light years away from the Milky Way. It was a separate galaxy... and now the measured universe was between 500 to 2000 times older than creationists would have us believe.

But M31 (also known as the Andromeda galaxy) is part of a group of galaxies called the Local Group. We were poised to solve one of the greatest mysteries of all time.

Sunday, August 21, 2011

The Age of the Universe: Part 2

Now that we have the local universe mapped pretty well, we can notice some things about the stars themselves. Once again, we use simple devices for measuring and cataloging stars.

One thing we can notice is that stars are different colors ranging from red to yellow to white to blue white. Now suppose we look at two white stars and measure that their color is almost exactly identical. We then figure the distance to these stars. One is twice as far away from Earth as the other. As we see it them from Earth, the more distant is one fourth as bright as the other. This fits in perfectly with the inverse square law of light.

What is the inverse square law of light? Simple, if you have a light source of known brightness (a candle for example) and move it away from the observer, it will dim in a predictable manner that is the inverse of the square of the distance. If a candle is one foot away from you and you move it two feet away from you, it will be one fourth as bright. Move it three feet away from you and it will be one ninth as bright... and so on. For an illustration and in-depth explanation of the inverse square law, click here.

Now by the same token, if you have two sources of light at different distances and they seem to be equally as bright to you the observer, they would have different brightnesses if they were the same distance from you. One candle one foot from you will give the same illumination as four candles two feet from you.

Fortunately, for those of us who want to measure the distances to the stars, we can see the the same law of physics applies to the stars as it does to candles. And the inverse square law of light is a pretty good thing, too. If the star Sirius (which was mentioned in the previous article) were as close as the sun, it would seem more than 23 times brighter.

Knowing that stars of the same kind have an intrinsic brightness gives us a yardstick for measuring the size of our home galaxy, the Milky Way. We could now measure our local universe to distances on the order of 100,000 light years. If we see something 100,000 light years away, we are seeing it as it was 100,000 years ago. This is two orders of magnitude older than the age of the universe as given by creationists. The calculations put forth by James Ussher in 1647 start to become questionable.

We haven't even left our galaxy yet and we can see that the universe is older than creationists would have us believe. We've barely started the journey.

We'll look at other galaxies along with the size and age of the entire universe in part 3.

Friday, August 19, 2011

The Age of the Universe: Part 1

I wrote a bit about the Traveling Creation Museum and its interesting (if not entirely convincing) curator, Sean Meek. I decided that I'd cool off a bit before saying too much and a couple years should be long enough.

Mr. Meek was talking about what astronomers know about the beginnings of the universe and he said that they simply "make things up." With that kind of statement, you might see why I wanted to calm down a bit before commenting further. He said other nonsensical things but this was the one that really got under my collar. He also belittled findings based on radioactive decay dating (potassium-argon decay for one). He tried to dismiss all of science under the blanket idea that because we weren't there, we can't know.

And it's true that there are no living witnesses who can attest to the existence of anything that happened more than 6000 years ago. I'll grant him that. But there is ample evidence that one needs only a brain, some simple math and a few simple scientific instruments that demonstrate that the universe in which we live is several orders of magnitude older than Mr. Meek would have you believe.

First, we figure out the distance to the moon. You can't tell by just looking at it and ancient people might have thought that if you stood on a high enough mountain, you could touch it (legends speak of such things). But determining the distance to the moon is actually pretty elementary. Set up a simple observatory. Set up a similar facility a known distance away (preferably a few hundred miles). Have your astronomers measure the angle between the moon and a nearby star. This gives you the parallax of the moon. Simple trigonometry and you have the distance to the moon, about 240,000 miles.

Second, now that we know how far away the moon is, we measure the distance to the sun. We know it's farther than the moon because it passes behind the moon during solar eclipses. We use the same sort of method we used to determine the distance to the moon. This time, it helps if we have accurate clocks to measure the angles because we can't use the stars (they're not out in the day time). But again, it's a matter of simple trigonometry to determine that the sun is about 93 million miles away.

Now with the work of Johannes Kepler and Isaac Newton, we can figure the orbits and the distances to the planets. We have the scale of the solar system which is about 8 billion miles from side to side (using the orbit of Pluto as sort of an edge... if we use the heliopause, it's bigger still).

Now we only need one observatory to go to our next level of measurement: the distance to the stars. We seek out a nearby star that can be seen in two different seasons, preferably opposite seasons (spring/autumn or summer/winter). Sirius is a good candidate. We measure its position against the background stars when it first starts appearing in the morning skies in August. Then we take a similar measurement the following February. We know that if we take these measurements 6 months apart, the two positions of the Earth will make a straight line with the sun in the middle. That line segment is about 186 million miles. Again, simple trigonometry and we find that Sirius is about 54 trillion miles away. It takes light a bit under 9 years to travel that distance so we say that Sirius is a little under 9 light years away (8.6 give or take 0.04 light years if you want to nitpick). We repeat this procedure for all the stars that are close enough for us to measure this way. That's about 100 light years which is right in our own backyard, celestially speaking. And that's a pretty huge number of stars when we see that there are about 50 stars within 17 light years of our sun.

Part 2 will discuss how we determine the distances to stars that we can't measure in this manner.

Wednesday, August 17, 2011

DM Revealed and Arrested

If you've ever read my blog, you might have seen a comment by a guy who signs his comments as DM. Apparently, he's gone way beyond the few bits of weirdness he's posted here. He's gone after PZ Myers, Michael Shermer, Phil Plait, Richard Dawkins among numerous others (I feel I'm in pretty good company).

He occasionally signed some of his posts as David Mabus but I found that his real name is Dennis Markuze. Normally, someone like this wouldn't even be a blip on my radar. However his rants on some sites have gone as far as death threats and someone finally decided to do something about it. He has been arrested for making these threats. The full story can be found HERE.

The picture in that article was taken at the Atheists Alliance International Convention when it was held in Montreal. Shortly after someone pulled a fire alarm, he was seen ranting and arguing incoherently with some of the convention's attendees. The fact that he would go to this convention to confront people face to face shows just how dangerous a person like this can be.

Do a quick web search for David Mabus and you'll see why I'm glad this person is in custody. He's a danger to others and to himself.

Labels: , , , , ,